should I go with 2.5 or 3'' to replace Resonator 2006 grandprix

2.5 inch will be much easier, or else your gonna have to do a lot more fab work. Your going to need over 3 feet of pipe to do it. Also, instead of clicking new topic when you reply, try clicking POSTREPLY

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2.5 should be plenty. Or you could go 2.25 then you wouldnt have to expand the piping

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DIY intake-HV3-3" catless dp-180 tsat-DIY shift kit-murphy custom tune

What is the deal in flippin the engine mounts is their any benefit and how would you flip them on 2006 grandprix

As Kaleb said, just get 2.25" if you really want to replace your res, but again there is no benefit in doing it. The stock exhaust system is not restrictive, especially if you're not boosted.

And yes, there is a benefit to flipping your front motor mounts. I'll go find the how to writeup.

Edit: Here you go.
97-03-grand-prix-discussion-f13/flipped-motor-mounts-t19315.html

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Dubs:00 VW GTI VR6, Low and Slow 91 VW GTI 8v, Shave the Bay!! 91 VW Cabriolet 8v, bitch Basket
GP's:04 GP GT, Past now G-Ma's Girlfriend's 97 GP GT, "Project Pink Power"